Synonyms:
- Chinese puzzle,
- baffling problem,
- brain twister,
- clincher,
- conclusive argument,
- crossword puzzle,
- crusher,
- crux,
- enigma,
- enigmatic question,
- finisher,
- jigsaw puzzle,
- knockdown argument,
- knot,
- knotty point,
- mind-boggler,
- mystery,
- nut to crack,
- perplexed question,
- perplexity,
- poser,
- problem,
- puzzle,
- puzzlement,
- puzzler,
- question,
- question mark,
- settler,
- sixty-four dollar question,
- sockdolager,
- sticker,
- stumper,
- tough proposition,
- vexed question,
- why